Method for making a medical electrode polymer

ABSTRACT

An electrode providing electrical contact with a patient&#39;s skin includes a conductive member adapted for connection to an external electrical apparatus and a non-liquid water containing film for electrically interfacing to said patient&#39;s skin, the non-liquid film being electrically and mechanically connected to said conductive member. The non-liquid water containing film includes an electrically conductive organic polymer plasticized with a polyhydric alcohol with said organic polymer being derived from a monomeric mixture comprising from about 2 to 30 pph acrylic acid, 2 to 30 pph of a glycolvinylether and 0.01 to 1.5 pph of a crosslinking agent. Preferably the polyhydric alcohol is glycerol.

The present application is a divisional of U.S. Ser. No 10/896,303,filed Jul. 21, 2004, now U.S. Pat. No. 7,252,792, which is a divisionalof U.S. Ser. No 10/256,653, filed Sep. 27, 2002, now U.S. Pat. No.6,842,636.

FIELD OF THE INVENTION

The present invention provides a combination electrode for use inmedical applications, e.g., medical applications requiring monitoringand stimulation and return of current, having an electrical currentconductor including a connector in addition to a skin-interfacing filmwherein this film may have adhesive, plastic and hydrophilic propertiessuch as may reside in an electrically conductive, polymeric composition.

BACKGROUND OF THE ART

Medical electrodes have, in the past, taken many shapes and forms.Principally, they have been shaped according to the use for which theyare intended. Electrodes used with monitoring apparatus, such as EKG andEEG machines, commonly have small round contact surfaces, whereaselectrodes used with such stimulation apparatus as pain control devicestend to be larger and have rectangularly and other conveniently shapedcontact surfaces. Whether intended for monitoring or stimulation use, adesign objective for each electrode group has been, and continues to be,good electrical signal transmission between a patient's skin surface andthe electrical cables connected to a particular piece of apparatus. Withrespect to stimulation and monitoring electrodes, efficient signaltransmission across the epidermis conductor interface is desirable.Further, with respect to stimulation electrodes, effective signaltransmission free of current concentration points or “hot spots” is alsodesirable.

Of the electrodes presently available, many offer combination structuresincluding a metallic or otherwise conductive support member to which anelectrical wire from an associated apparatus may be attached.

Certain of the currently available electrodes, including electricalstimulation electrodes are disclosed in U.S. Pat. Nos. 4,722,354;4,736,752; 4,819,328; 5,038,796 and 5,450,845 to Axelgaard et al whichare hereby incorporated by reference to show various electrode designsincluding but not limited to medical electrode shapes, structures,materials and methods for connecting said medical electrodes to theappropriate electrical apparatus.

In many instances, the medical electrodes of the prior art need theaddition of generous amounts of an electrode paste or gel applieddirectly to the conductive support member to enhance conductivity acrossthe skin-electrode interface to the point where acceptable operatingconditions are achieved.

Other prior art electrodes teach the incorporation of an open cellularskin interface pad secured to a conductive support member. This pad, asshown in U.S. Pat. No. 3,817,252, is often sponge material whichfunctions to hold an amount of electrolyte solution in order to enhanceconductivity across the skin-pad interface. Such an interface pad canbe, alternately, saturated with electrode pastes or gels of the typethat do not run or evaporate as readily as electrolyte solutions.

The prior art elect-codes that require an electrode paste or gel orelectrolyte solution provide a structure which does not always maintainconstant, efficient and effective electrical transmission for longperiods of time without the need for additional electrode paste, gel orsolution. Moreover, there is a tendency while using these electrodes,for the electrode gel to separate and/or to flow to a nonuniformthickness. Under these conditions, sections of the conductive supportmember could be exposed to the skin and local hot spots can result whichcan cause discomfort if not severe enough to cause burns to thepatient's skin. Therefore, medical electrodes wherein the adhesive,itself, provides the conductive interface between the skin and theelectrical connector are very desirable. An electrode of this type isdisclosed in U.S. Pat. No. 4,066,078 to Berg. In this patent, thepolymer itself acts as the adhesive and, through the quaternary groupsattached to the polymer backbone, provides a conductive interface.

Nevertheless, others have continued to formulate adhesive materials thateffectively adhere to the skin and the materials that can be utilized infabricating a medical electrode and also provide adequate conductivity.See, for example, U.S. Pat. Nos. 4,830,776; 4,274,420; 4,777,954;4,699,146; 4,158,696; 5,024,227; 4,243,051; 6,115,625, etc., whichexemplify the continuing search for conductive adhesive materials foruse in medical electrodes.

Acrylic hydrogels are commonly used biomedical hydrogels due to lowcost, absorbency, and ease of fabrication. These hydrogels may be usedas contact lens materials as disclosed in U.S. Pat. No. 5,712,356 and asconductive electrode adhesives as disclosed in U.S. Pat. No. 5,868,136.

Vinyl ether monomers are biocompatible and environmentally friendly, andglycol vinyl ether monomers are water-soluble. Vinyl ether homopolymersare also flexible and elastic. The only commercial method of vinyl etherhomopolymerization is cationic and can not be done in the presence ofwater.

It has now been found that the free radical copolymerization of glycolvinyl ether monomers with acrylic monomers in water promotes a highdegree of acrylic polymerization and imparts greater flexibility andelasticity to the resulting acrylic copolymer than other co-monomers.Moreover, as compared to acrylic hydrogels without copolymerized glycolvinyl ether, copolymers of acrylic acid and a glycol vinyl ether providefilms that are softer, has less aggressive adherence to skin andseparate from skin without stringing or leaving residue on the skin.

However, a major problem that had to be overcome was that water-solubleacrylic monomers hydrolyze glycol vinyl ether monomers at the optimumconditions for free radical polymerization. A by-product of thishydrolysis is an irritating aldehyde. This problem has been solved bythe present invention by reacting these aldehydes into biologicallybenign compounds. The amount of irritating residual acrylic monomers isalso reduced by the high degree-of-polymerization of the electrodeadhesives of this invention.

An objective of this invention, therefore, is to provide an electrodewith an improved electroconductive skin-interface substrate, which willperform a similar function to, and eliminate the need for, anelectrolyte solution, electrode paste or electrode gel.

Another objective of this invention is to provide an electrode with askin-interface substrate having pressure sensitive adhesive propertieswhich will enable the electrode to adhere to the skin without the use oftape or other securing mediums.

Another objective of this invention is to provide an adhesive substratethat has high tack so that minimal pressure is needed to apply it to theskin but is such that it can also be easily separable from the skin uponremoval without any noticeable residue.

A further objective is to provide an electrode with a non-liquidskin-interface which is a film which will maintain a uniform thicknessand will not separate to expose sections of a conductive support memberto the skin.

Yet another object is to provide an electrode with an electroconductiveskin-interface that will not dry out or decomposed for period of yearseven if exposed to the atmosphere.

An even further objective is to provide an electrode having askin-interface substrate which will not decompose or dry out likeelectrodes utilizing electrolyte solutions under long periods of use.

Other objects and advantages of the present invention will becomeapparent from a careful reading of the specification below.

SUMMARY OF THE INVENTION

The objectives of this invention are accomplished in a medicalelectrode, suitable for stimulation, monitoring applications and returnof current, including an electrically conductive member capable of beingconnected to an external electro-medical apparatus. This conductivemember may be a pliable sheet of material preferably having connectedthereto a medium for securing positive electrical connection between theconductive member and the external electro-medical apparatus. Attachedto the underside of the conductive member and extending away from theelectrical connection is an electrically conductive skin-interfacesubstrate material, preferable in the form of a film. This material musthave adhesive properties so that it will adhere to the skin of apatient. Preferably, this material also has plastic and hydrophilicproperties. A suitable combination of the aforementioned adhesive,plastic and hydrophilic properties is provided by an adhesivecomposition which comprises an electrical conductive organic polymerplasticized with a polyhydric alcohol, e.g., glycerol.

Suitable electrically conductive organic polymers useful in the adhesivecomposition utilized in the medical electrode of the present inventioninclude copolymers derived from the polymerization of acrylic acid and aglycol vinylether. Such copolymer may further include the followingcomonomers: 2-acrylamido propane sulfonic acid, methylene-bisacrylamideand acryloxyethyl dimethyl ammonium chloride and other cationic acrylicesters.

The adhesive composition may also include an aldehyde reactant such as,but not limited to, hydrogen peroxide, 2-hydroxyethylethylene urea (HEU)or L-arginine hydrochloride.

The precursor to said adhesive composition is copolymerized to yield afilm having suitable adhesive properties and electroconductivityproperties for use as a medical electrode adhesive in the presence of anultraviolet sensitive curing agent such as2-hydroxy-2-methyl-1-phenyl-propan-2-one (available as Darocure 1173®),4-2-hydroxyethoxy)-phenyl-(2-hydroxy-2-phenyl-(2-hydroxy-2-propyl)ketone(available as Darocure 2959®), or 2,2-dimethoxy-2-phenylacetciphenone(available as Irgacure® 651)1-[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one (asavailable as Irgacure® 2959) and trimethyl benzoyldiphenylphosphineoxide (available as Esacure DP250) or 1-hiydroxycyclohexylphenyl ketone(available as Irgacure 184.) (Other initiators are disclosed in U.S.Pat. Nos. 5,800,685, 6,115,625 cited above). These patents areincorporated herewith in their entirety by this specific referencethereto.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more readily understood by reference to thedrawings wherein like numerals refer to like elements and in which:

FIG. 1 shows a perspective view of the electrode; and

FIG. 2 shows a cross-section in side elevation through the electrode ofFIG. 1; and

FIG. 3 is a texture analysis plot.

DETAILED DESCRIPTION OF THE INVENTION

Medical electrodes are intended for usage as efficient and effectivetransmission mediums between a patient's skin and an electro-medicalapparatus. Primary to their operation is a uniform conductivity throughthe electrode itself and a uniform conductivity across the electrodeskin-interface. Uniform conductivity through an electrode is most ofteninterrupted by a non-uniformity in the electrode materials. Uniformconductivity across the electrode skin-interface is most ofteninterrupted by a separation of some or all of the electrode interfacingmaterial in contact with a patient's skin.

Preferably, the electrode is intended to be disposable. It is alsointended to have adhesive properties sufficient to be self-adhering to apatient's skin for weeks without drying out. In fact, the adhesiveproperties of the gel in accordance with the present invention have beenmaintained for more than 3 years, without drying out. However, the gelhas sufficient flexibility and elasticity to move as a patient's skinmoves while returning to original shape when permitted. Additionally, itis intended to provide uniform conductivity with even current densitiesof approximately 30 microamperes per square millimeter when subjected toa stimulus of about 60 milliamperes at 35 cycles per second having apulse duration of about 250 microseconds. This electrode is intended tobe easily handled, non-irritating to a patient's skin, and sterilizable.

The electrode configuration is shown in FIG. 1. A conductive member 11is cut, stamped or otherwise shaped out of a piece of conductivematerial which may be aluminum foil or a polyester, e.g., a polyethyleneterephtalate (Mylar®) coated with aluminum or tin. The shape to whichthis conductive member 11 is formed will depend upon the particularapplication in which it is to be used. The shape is sometimes round butmay be as shown in FIG. 1, rectangularly shaped.

Alternately, other metallic foils, conductive polymers, graphitized ormetallized cloth or wire mesh may be used as the conductive member. Inparticular, the knit conductive fabric disclosed in U.S. Pat. No.4,722,354 may be utilized as the conductive member. For each material,an appropriate strength and thickness is to be chosen to yield apliable, yet sufficiently strong member 11. When the conductive member11 is of aluminum foil, it usually is of 1-10 mil thickness.

Secured to the outer surface of the conductive member 11 is a connector13 for providing a medium to which external signal cables may beattached for electrically communicating with the conductive member 11.This connector 13 may be a conductive swaged snap fastener 13, as shownin the accompanying drawings, which is available commercially. Thisfastener 13 is mechanically and electrically attached to the conductivemember 11, extending perpendicularly from the outer surface of thismember 11. Alternatively, when the conductive member is a knitconductive fabric, the electrical connector may be stranded stainlesssteel as shown in U.S. Pat. No. 4,722,359.

Abutting the inner surface of the conductive member 11 is anelectrically conductive skin-interface substrate 15. This substrate 15is a layer of material being typically a film or sheet which will bedescribed below.

The conductive substrate 15 is shaped correspondingly to the conductivemember 11. When constructed in combination with a rectangular member 11,the substrate 15 is also rectangular. The film thickness of thissubstrate 15 is uniform throughout, however, this uniform film may be ofvarious thicknesses. A range of 10 to 100 mils, e.g., about 50 mils iscommon.

As will be discussed below, the substrate 15 is a film or sheet havingadhesive properties, thus when it is brought into contact with theconductive member 11, it will adhere to that member 11 providingelectrical connection with it.

A supporting scrim 17, FIG. 2 may be used in electrode configurationswhere a greater thickness substrate 15 film is used. This scrim 17,while not a necessary part of the electrode, will tend to support bybeing distributed throughout the substrate 15. A further advantage tothe use of this scrim 17 is that it acts to reinforce and strengthen thesubstrate 15.

The scrim 17 is positioned within and through the thickness of thesubstrate 15, in alignment with the conductive member 11, and is of asize to extend completely under the conductive member 11. The scrim 17can be a woven or non-woven spun-bonded polyester fabric, a net of astretched, embossed melt-extruded polymeric film, a sheet of polyolefinmonofilaments heat-sealed together at their interstices, a thin sheet ofa thermoplastic polymer with holes heat-stamped in a geometric patternor any other supportive media. The scrim 17 may be any material allowingtransmission of light for curing if only cured from one side. Also, thescrim 17 should retain most of its strength when wetted by the monomericmixture.

In operation, the electrode is applied with the substrate 15 in directcontact with the skin. The adhesive properties of the substrate 15eliminate the necessity for tape or other securing mediums to hold theelectrode in continuous contact with the skin. The swaged fastener 13,or other suitable connector, receives electrical signals from anexternal apparatus. These signals are conducted into the conductivemember 11 which in turn directly conducts them into the substrate 15. Inthis manner, current densities are uniformly distributed over the areaof the substrate 15 in contact with the conductive member 11 and, inturn, are uniformly transmitted to the skin surface in contact with thesubstrate 15.

Primary to the unique structure of the electrode for eliminating theneed for added electrode pastes, gels or electrolyte solutions, and foreliminating the need for securing mediums to hold the electrode inplace, are the composition and structure of the substrate 15 material,enabling it to possess the desired physical, chemical and electricalproperties.

Substrate 15 is a sheet or film of an electrically conductive organicpolymer plasticized with a polyhydric alcohol, preferably glycerol.

The electrically conductive organic polymers that are utilized inpreparing substrate 15 are derived from the copolymerization of amixture of monomeric acrylic acid and a glycolvinyletiher. Said organicpolymer may comprise 10 to 75 parts per hundred, by weight (pph), e.g.,30 to 60 pph, acrylic acid and 75 to 25 pph, e.g. 70 to 40 pph, of aglycolvinylether. In addition, the above mixture of comonomers, theorganic polymer, may further include additional comonomers; inparticular, the acrylic acid may be completely or partially replacedwith AMPS.

Preferably the glycolvinylether may be selected from the groupconsisting of hydroxybutyl vinyl ether ethyleneglycolvinylether,diethyleneglycolmonovinylether, and triethyleneglycolmethylvinylether.Most preferably the glycolvinyl ether is diethylene glycol monovinylether.

Furthermore, the organic polymer may comprise about 0.01 to 1.5 pph of acrosslinking agent, such as methylene bisacrylamide, to increase themolecular weight and cohesivity of the conductive organic polymerthrough crosslinking. Other comonomers having at least twocopolymerizable olefinic moeities, especially difunctional ortrifunctional derivatives of acrylic acids, may be utilized. Forexample, polyethylene glycol dimethacrylates and diacrylates having amolecular weight of from about 200 to about 600 and ethoxylatedtrimethlolpropane triacrylate (ETMPTA) are preferred is crosslinkingagents.

The comonomer mixture that is copolymerized to provide the conductiveorganic polymer will also include a polyhydric alcohol, e.g.,polyhydroxyhydrocarbons and oxyalkyls, e.g., polyetheneglycol, sorbitol,glycerol, etc. to plasticize the organic polymer. The polyhydricfunctions as a humectant, i.e., it absorbs moisture and promotesconductivity of the substrate 15. The polyhydric alcohol may comprisefrom 25 to 75 pph, preferably from 40 to 60 pph, e.g., about 37 to 53pph of the comonomer mixture. Most preferably, the polyhydric alcohol isglycerol.

The comonomer mixture that is copolymerized to provide the conductiveorganic polymer may also include a thickening agent. The thickeningagent may be a high molecular weight polymer or copolymer such as aN-vinylpyrrolidone/vinylacetate copolymer (Luviskol VA 73W or VA 64W)available from BASF; methylvinylether/maleic anhybrid copolymer(Gantrez® S95), which is available from ISP; ethylene/maleic anhydride(EMA) Copolymer, which is available from Zeeland Chemical; andN-vinylpyrrolidone/acrylic acid Acrylidones (ACP-1041 or Acrylidone1005), which is available from ISP, and may comprise from about 0.5 to 8pph of the comonomer mixture, e.g., about 2 to 5 pph. The N-vinylpyrrolidone/vinylacetate copolymer disclosed above is especiallypreferred for use in the compositions of this invention.

Magnesium acetate may also be included when the electrode is utilized asa stimulating electrode. Potassium chloride may be added when theelectrode is utilized as a sensing electrode.

The above comonomer mixture is preferably copolymerized or cured bythermal or ultraviolet (UV) radiation. Therefore, an ultravioletsensitive curing agent is provided in the comonomer mixture at aconcentration of from 0.05 to 3 pph, preferably from 0.5 to 2.0 pph.Suitable curing agents are 2-hydroxy-2 methyl-1-phenyl-propan-2-one(available as Darocur 1173®), 4-(2-hydroxyethoxy)phenyl(2-hydroxy-2-phenyl (2-hydroxy-2-propyl)ketone (available as Darocure2959™), 2,2-dimethoxy-2-phenyl acetophenone (available as Irgacure®651), 1-[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one(available as Irgacure® 2959) or 1-hydroxycyclohexylphenylketone(available as Irgacure 184), all of which are available from Ciba-Geigyand trimethyl benzoyl diphenyl phosphine oxide (available as EsacureDP250).

Thus, to prepare the substrate 15, the following gelled comonomermixtures may be subjected to thermal or ultraviolet polymerizationconditions:

Broad Preferred Ingredient Range pph Range pph acrylic acid  2-20  4-12glycolvinylether  2-20  3-10 crosslinker 0.01-3   0.01-2.0  thickener0-8   0-3.0 glycerin 25-75 35-60 UV sensitive curing agents 0.5-3  0.5-1.5 distilled water 10-40 15-30

The acrylic acid is preferably partially neutralized with a basicpotassium or sodium oxide, hydroxide, or carbonate or amine, e.g.triethanolamine. For example, from 25 to 75 molar percent acrylic acidmay be neutralized.

A buffer may also be included in the comonomer mixture, e.g. from 0.2 to2 pph of potassium sodium tartrate, or aluminium potassium sulfate (afurther function of the AL⁺³ ion of the above buffer and Mg⁺² ions, aswell, is that such ions function as firming agents for the compositionsof this invention).

Finally, an aldehycie reactant or neutralization agent may be includedto remove any aldehyde generated by the acid hydrolysis of the vinylether monomer. Suitable aldehyde reactants include hydrogen peroxide,e.g. from about 1 to 3 pph; 2-hydroxyethylethylene urea, e.g. from about1 to 5 pph; and L-arginine hydrochloride, e.g. from about 1 to 5 pph.Most preferably the aldehyde reactant is 2-hydroxyethylethylene urea atfrom 3 to 5 pph.

The above conductive substrate has a capacity for absorbing andretaining large amounts of water. This property further promotes theconductivity of the copolymer.

As previously mentioned, while the above disclosed substrate will absorblarge amounts of water, it is substantially insoluble in water becausethe conductive organic polymer contains at least 0.02 parts by weightper 100 parts of monomer of a crosslinking agent.

The substrate 15 compositions exhibit a tackiness which can be increasedas the glycerol concentration is increased. As water and/or salt wateris absorbed, the surface of the substrate material 15 softens. As aresult, the substrate 15 will flow into pores and other irregularitiesin the skin, creating a mechanical interlock bond with the skin inaddition to the already present adhesive bond. The bonding and,concomitantly, the electrical transmission of the electrode are enhancedas it “ages” in contact with the skin.

Importantly, the flexibility and elasticity of the substrate imparted bythe glycol vinyl ether co-monomer make it appear that the substrate 15never dries out. Actually, the water content does go up and down withthe ambient humidity but it is not apparent to the user because thephysical properties remain relatively unchanged. Enough water isretained that the electrode remains electrically functional even in dryconditions for months or years as hereinafter reported.

The UV free radical polymerization reaction of acrylic acid and glycolvinyl ether is so strongly driven that relatively large amounts ofglycerol can be incorporated compared to other UV cure hydrogels. [Alsothe acrylic acid can be completely reacted in the presence of glycerolif the proper amounts of glycol vinyl ether and UV initiator are used.]This is to be compared with prior art substrates which typically containabout 20%-40% walter and little or no glycerol causing drying to occurwithin hours.

The flow condition eliminates air spaces between the skin and thesubstrate 15 to greatly reduce the impedance across the interface. Thisin turn greatly reduces the heat normally created at this interface.While the surface portion of the substrate 15 will flow, the greaterportion of its mass will remain intact. Thus, the material resistsseparation or the development of irregular thicknesses. As a result, twoheat and/or burn producing conditions, i.e., a high resistance acrossthe interface due to an air layer which creates high temperatures overthe entire interface, and the physical contact of the conductive member11 directly to the skin creating a shunt of the( current to a small areaand generating extreme temperature in that area, are avoided.

A secondary electrical effect is also improved as the electrode “ages.”Present during the operation of all electrodes is a battery effectcreated at the skin interface due to the capacitance across thisinterface. This battery effect causes some current to tend to circlebackward towards its source of flow creating eddy currents. With thiselectrode of the invention, as water and body salts are absorbed intothe electrode substrate, the interface area becomes more ionically(i.e., electrically) homogenous, thus reducing the battery effect andany resulting eddy currents.

The electrode may be packaged for use in a sealed or unsealed envelopeof any of a number of suitable materials such as polyethylene or otherplastic film. Foil barrier packaging, as used with prior art electrodes,is not required for the present invention. Packaging of the presentinvention is only required for product identification and to preventcontamination. In that regard, a release paper or film of a waxed orplastic-coated type can be used to protect the substrate 15 beforeapplication to a skin surface.

The invention is further illustrated by the following examples which areillustrative of a specific mode of practicing the invention and is notintended as limiting the scope of the appended claims.

EXAMPLE I

Acrylic acid and glycol vinyl ethers copolymerize via a charge transfercomplex wherein the vinyl ether acts as an electron donor and theacrylic acid acts as an electron acceptor. This reaction occurs in amatter of minutes if just these two materials are mixed togethergenerating very low molecular weight species; however, high molecularweight species (>10,000) can be created with a free radical initiator.Molecular weights should be greater than about 100,000 daltons to beadhesive and leggy and less than about 5,000,000 daltons, as a highermolecular weight may be too firm at the level of crosslinking preferred.Mixing and curing of the ingredients, utilized in the below examples,must be done quickly to avoid the generation of a significantconcentration of aldehydes from the acid hydrolysis of the vinyl etherby the acrylic acid and to avoid generation of low molecular species byautopolymerization.

The following formulation is utilized as a conductive substrate. Thisformulation is prepared as follows: Into a stainless steel mixingcontainer, equipped with a mechanical stirrer, is added 62.4 g ofdeionized water. With slow agitation, 3 g of sodium hydroxide and 6 g ofpotassium chloride are slowly added to the water. After allowing thestirred caustic solution to cool to room temperature, 48 g acrylic acid,24 g of diethyleneglycolmonovinylether, 150 g of glycerin and 2.7 g of a1% solution of methylene-bisacrylamide, in that order, are slowly addedto the water containing solution. The resulting mixture is stirred foran additional 15 minutes while the solution is purged with a slow streamof nitrogen gas to displace the residual dissolved oxygen gas from thesolution. Finally, a mixture of 0.9 g of CN 383 and 3 g of Irgacure® 184is poured into the stirred water containing solution. The resultingmixture is coated on and penetrates a polyester scrim, such as Reemay®1006 or 2250 to provide a coating thickness of between 10 to 100, e.g.,about 40 to 60 mils. Typical line speeds for the coating process varyfrom 10 to 100, e.g., 30 to 60 linear feet per minute. The coatedpolyester scrim is irradiated with ultraviolet radiation from a UVsource, such as the electrodeless microwave energy activated curingsystem available as the I-600-M from Fusion Systems Corporationoperating at from 400 to 600 watts/inch.

The cured composition is subject to testing for adhesivity (i.e., thebond between the scrim reinforced gel and a substrate, e.g., a standardstainless steel plate or possibly the Mylar® film web upon which thescrim reinforced gel is coated prior to being irradiated), using theSatec T1000 material Testing Machine (SATEC Systems, Grove City, Pa.)equipped with an adjustable tilt table set for 90°. The test procedurefor 90° peel strength requires the pulling of a one-inch-wide strip ofgel from the substrate (stainless steel plate or Mylar° web) at 12inches/minute and at an angle of 90′ to the plane of the sample as perASTM D1876, ASTM D3330M (American Society for Testing Materials,Philadelphia, Pa.) or PSTC-1 and -3 (Pressure Sensitive Tape Council,Glenview, Ill.), and recording the average peel force in grams/oneinch-width. (ASTM D3330M and PSTC-1 and -3 are for 180° peel testing butwere adapted for use in this Example.)

The formulations of Table 1 are prepared similarly, except that variousdifferent ingredients may be utilized as specifically noted in Table 1.

Certain of the ingredients (components) of the formulations of Table 1are as follows:

Irgacure ® 2959 Photoinitiator available from Ciba Specialty ChemicalsSR-9035 15-mole ethoxylated trimethylol propane triacrylate fromSartomer Actilane 755 Amine synergists available from Akzo Actilane 705Nobel Chemicals America CN 373 Reactive amine coinitiators available CN383 from Sartomer SR 511 2-Hydroxyethlethylene urea available FromSartomer Hawaiian Blue Available from Chefmaster ® FA1Q80BCAcryloxyethyl dimethyl ammonium Chloride available from Ciba Neodox ™25-11 Alcohol ethyl carboxylate available From Hickson DanChem ESACUREDP-250 Photoinitiator Mixture available from Lamberti

The compositions of the present invention are suitable for fabricating amedical electrode that accomplish the objects of this invention, i.e.the compositions of Table I are soft hydrogels, adhesive to human skin,and having the requisite flexibility and elasticity. The compositions ofTable 1 are softer, low

NOTE BOOK NUMBER COMPONENT 21-59B 23-06B 23-26 23-38A 23-43C 23-87A23-88A 23-88B 28-92 31-81B 41-33B 51-10 51-30 COMPONENT D.I Water 20.80%21.80% 23.20% 21.00% 21.70% 24.50% 25.50% 24.50% 17.10% 18.10% 17.50%16.30% 19.10% D.I Water Magnesium Acetate 2.00% Magnesium AcetateTriethanolamine 99% 1.10% 7.50% 7.70% Triethanolamine 99% Glycerin50.00% 50.00% 50.00% 50.00% 50.00% 50.00% 50.00% 50.00% 54.00% 46.00%49.00% 48.00% 48.00% Glycerin UREA 511 2.00% 3.00% 3.00% 3.00% 4.50%5.00% 4.45% 4.40% UREA 511 PVP/VA K-90 2.00% PVP/VA K-90 FA1Q80BC 12.00%FA1Q80BC Acrylic Acid 16.00% 12.00% 12.00% 12.00% 12.00% 12.00% 12.00%12.00% 3.40% 10.00% 11.00% 11.00% 11.00% Acrylic Acid *DEGMVE 8.00%6.00% 6.00% 6.00% 6.00% 6.00% 6.50% 10.06% 8.80% 8.60% *DEGMVE 50%Sodium AMPS 7.00% 50% Sodium AMPS Potassium Chloride 3.00% PotassiumChloride Potassium Alum 0.20% Potassium Alum Sodium Hydroxide 3.50%3.00% 3.00% 3.00% 3.00% 3.00% 3.00% Sodium Hydroxide K—Na Tartrate 1.00%1.00% 1.00% 1.00% 1.00% 1.00% 1.00% 1.00% K—Na Tartrate HydrogenPeroxide 2.00% 2.00% Hydrogen Peroxide L-Arginine (pure) 4.00%L-Arginine (pure) Glycine 4.00% Glycine **TMVE 4.00% **TMVE ***EGVE3.00% 4.00% ***EGVE K2HPO4 1.50% K2HPO4 NaH2PO4 0.60% NaH2PO4 50% NaOH4.00% 4.00% 50% NaOH Hawaiian Blue 0.50% 0.50% 0.50% 0.50% 0.30%Hawaiian Blue NVP 2.00% NVP 3% I-184 (in IPA) 1.00% 1.00% 1.00% 1.00%1.00% 1.00% 1.00% 1.00% 1.00% 3% I-184 (in IPA) Irgacure 2959 0.20%Irgacure 2959 Tin Octoate 0.10% Tin Octoate SR-9035 0.06% 0.03% 0.03%SR-9035 1% MBA (in water) 0.80% 2.00% 1.20% 1.50% 0.90% 1.00% 1.00%1.00% 2.00% 1% MBA (in water) MBA 0.10% MBA CN-383 0.30% 0.70% 0.60%0.50% 0.40% 0.50% 0.50% 0.50% 0.50% 0.20% CN-383 Actilane 755 0.10%Actilane 755 DP-250 0.08% 0.17% 0.17% DP-250 Actilane 705 0.15% 0.15%Actilane 705 CN-373 0.30% CN-373 Neodox 25-11 0.05% Neodox 25-11 100.00%100.00% 100.00% 100.00% 100.00% 100.00% 100.00% 100.00% 100.00% 100.00%100.00% 100.00% 100.00% *DEGMVE Diethyleneglycol monovinyl ether **TMVETri(ethylene glycol)methyl vinyl ether ***EGVE Ethylene glycol vinyletherin adhesion, and leggy as compared to similar compositions without aglycol vinyl ether component.

As an example, composition 51-30 was evaluated in a Texture AnalyzerStudy as described in TA, XT 2i Texture

Analyzer Study: Sealants & Caulking for Bath and Kitchen Study #I-92available from Texture Technologies Corp. of Searsdale, N.Y., which ishereby incorporated by reference and made a part of this specification.The results are shown in FIG. 3.

The Texture Analyzer is a probe that pushes into the gel then pulls outof the gel. The graphs are plots of Force vs. time. The first peaks A¹,A², A³, A⁴ represent the force of resistance to compression and theareas under the peaks represent the compressive work done to penetrate40% of the gel thickness. The second peaks B¹, B², B³, B⁴ under thebaseline are the maximum adhesive forces and the areas under the peaksrepresent the adhesive work. If there are two adhesive peaks, the gel isyielding (narrowing and possibly stringing). When the gel lets go, theplots go back to baseline.

In FIG. 3, a composition (51-30) of this invention (plot 1) is comparedto on acrylate copolymer gel comprising a sodium salt of 2-acrylamidopropane sulfonic acid and sodium salt of acrylic acid (plot 2). Ascompared to the pure acrylate gel, the composition of this invention issofter, as shown by the smaller late peak, which is the compressionforce peak, lower in adhesion, as shown by the small flat peak, andleggy, as shown by the time of release i.e. it holds onto the probe thelongest, see plot segment 1 a. The composition of this invention rollsoff the probe in a wave without yielding.

Also shown in FIG. 3 is plot 3 representing composition 51-97, (noDEG,MVE) and plot 4 representing a polyvinyl pyrrolidone adhesiveavailable from Valley Lab, Inc. As shown both plots 3 and 4 have agreater and shorter peak A², A³ and peaks B², B³.

EXAMPLE II

The compositions designated 23-38A in Table I, above, was tested forbiocompatibility in the following tests:

An in vitro biocompatibility study, based on the United StatesPharmacopea (USP) guidelines, was conducted on a test article, i.e.Composition 23-38, to determine the potential for cytotoxicity. A 1.0cm² portion of the test article, the negative control, and the positivecontrol were each placed on duplicate agarose surfaces directlyoverlaying confluent monolayers of L-929 mouse fibroblast cells. Afterincubating at 37° C. in 5% CO₂ for 24-26 hours, the cell cultures wereexamined macroscopically for cell decolorization around the test articleand controls to determine the zone of cell lysis (if any). The cultureswere then examined microscopically (100×) to verify any decolorizedzones and to determine cell morphology in proximity to and beneath thetest and control articles.

Under the conditions of this study, the test article showed no evidenceof causing cell lysis or toxicity. The test article met the requirementsof the USP. The negative and positive controls performed as anticipated.

The test article, Composition 23-38A, was evaluated for primary skinirritation in accordance with the guidelines of the InternationalOrganization for Standardization 10993: Biological Evaluation of MedicalDevices, Part 10: Tests for Irritation and Sensitization. Two 25 mm×25mm sections of the test article and control article were topicallyapplied to the skin of three rabbits and left in place for 24 hours. Thesites were graded for erythema and edema at 1, 24, 48 and 72 hours afterremoval of the single sample application.

Under the conditions of this study, no irritation was observed on theskin of the rabbits. The Primary Irritation Index for the test articlewas calculated to be 0.0. The response of the test article wascategorized as negligible.

A study was conducted in the guinea pig to evaluate the potential fordelayed dermal contact sensitization of Composition 23-38A. The studywas conducted based on the requirements of the InternationalOrganization for Standardization 10993: Biological Evaluation of MedicalDevices, Part 10: Tests for Irritation and Sensitization.

The test article was occlusively patched for 6 to 8 hours to the intactskin of 10 guinea pigs, three times a week, for a total of nineinduction treatments over a 3 week period. The control article wassimilarly patched to 5 guinea pigs. Following a recovery period, the 10test and 5 control animals received a challenge patch of the testarticle and the control article. All sites were observed for evidence ofdermal reactions at 24, 48, and 72 hours after patch removal.

Under the conditions of this study the test article showed no evidenceof causing delayed dermal contact sensitization in the guinea pig.

It is well known that acrylic gels in general do not perform adequatelyin the above tests particularly cytotoxicity. (R. Schwalm, et al.,“Vinyl Ethers in UV Curing: Copolymers With Acrylates and UnsaturatedPolyesters”; Conf. Proc Rad Tech Europe 99; Berlin, Germany; Nov. 8-10,1999, p 103-109)

The acrylic acid-glycol vinyl ether gels of the present inventionachieve perfect scores in the above tests.

In human wear testing on 20 persons (10 male, 10 female) no skinreaction was noted. Three of test subjects have been sensitized toacrylic hydrogel, and experienced no skin reaction to the presentinvention.

In addition, the gels of present invention have no apparent drying afterexposure to the atmosphere between a few days and up to about at least 3years or longer.

It is noted that the biggest problem that had to be overcome inpreparing the above Examples was vinyl ether monomer hydrolysis. Thereis little basic hydrolysis but there is neutral and substantial acidichydrolysis with acidity determining the rate. This presented a majorimpediment when acrylic acid was utilized as a comonomer with a glycolvinyl ether since acrylic acid polymerization is more effective as thepH is lowered. (See U.S. Pat. No. 5,352,713 at column 5, lines 10 and11, wherein it is stated that acid moieties react with vinyl ethers evenin non-water containing systems such as the free radical co-polymerizedacrylate-vinyl ether polymer coatings disclosed therein.) Thus, thepolymerization reaction is carried out, preferably, at a pH of fromabout 3.5 to 5.5 to yield a gel having a pH of from about 3.8 to 6.7.

While particular embodiments of the invention have been described, itwill be understood, of course, that the invention is not limited theretosince many obvious modifications can be made and it is intended toinclude within this invention any such modifications as will fall withinthe scope of the appended claims. For example, it will be appreciated,by those skilled in the art that other alkaline materials can beutilized to neutralize the acrylic acid monomer, e.g., mono and polypositive alkaline materials, e.g., sodium, potassium, calcium,magnesium, aluminum basic oxides, hydroxides or carbonates may be usedas well as ammonium hydroxide, etc.

Other thickeners or viscosity increasing agents which may be used in themedical electrodes of the present invention include polyacrylamide,polyvinyl alcohol, polyacrylic acid, polyethylene oxide, methylcellulose, ethyl cellulose, carboxymethyl cellulose, hydroxyethylcellulose and polyacrylamide-alkylsulfonic acid.

Finally, the conductive polymer may include particulate reinforcingagents and/or fillers, such as silica, e.g. Cabosil®.

1. A method of making a conductive organic polymer plasticized with apolyhydric alcohol and suitable for electrically interfacing to apatient's skin in a medical electrode which comprises polymerizing amonomeric mixture comprising 2 to 30 pph acrylic acid, 2 to 30 pphglycol vinylether, 0.01 to 1.5 pph of a crosslinking agent, and saidpolyhydric alcohol in the presence of an ultraviolet sensitive curingagent, and water.
 2. The method of claim 1 wherein said polymerizationis carried out at a pH of from about 3.5 to 5.5.
 3. The method of claim1 wherein said polymerization is carried out in the presence of analdehyde reactant or neutralizer.
 4. The method of claim 1 wherein saidpolyhydric alcohol is glycerol.
 5. The method of claim 4 wherein saidcrosslinking agent is selected from the group consisting of methylenebis-acrylamide and polyethylene glycol diacrylates and dimethacrylateshaving a molecular weight from about 200 to about
 600. 6. The method ofclaim 5 wherein said crosslinking agent is ethoxylatedtrimethylolpropoane triacrylate(ETMPTA).
 7. The method of claim 4wherein said glycolvinylether is selected from the group consisting ofhydroxybutylvinylether, ethyleneglycolvinylether, diethylene glycolvinylether, and triethyleneglycolmethylvinylether.
 8. The method ofclaim 7 wherein said glycol-vinylether is diethylene glycol vinyl ether.9. The method of claim 7 wherein said monomeric mixture furthercomprises from about 35 to 60 pph of glycerol.
 10. The method of claim 9wherein at least a portion of said acrylic acid is replaced with2-acrylamido propane sulfonic acid (AMPS) or a cationic acrylic ester.11. The method of claim 1 wherein said monomeric mixture furthercomprises from 0.01 to 3 pph of an ultraviolet sensitive curing agent.12. The method of claim 11 wherein said ultraviolet sensitive curingagent is selected from the group consisting of2-hydroxy-2-methyl-1-phenylpropan-2-one, 4-(2-hydroxyethoxy)phenyl(2-hydroxy-2-phenyl-2-hydroxy-2-propyl)ketone,2,2-dimethoxy-2-phenyl-acetophenone 1-[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one, 1-hydroxycyclohexylphenyl ketone, trimethyl benzoyl diphenyl phosphineoxide and mixtures thereof.
 13. The method of claim 12 wherein saidmixture comprises from 5 to 25 pph acrylic acid and from 5 to 25 pph ofa glycolvinylether.
 14. The method of claim 13 wherein saidglycolvinylether is selected from the group consisting ofhydroxybutylvinylether, ethyleneglycolvinylether, diethylene glycolvinylether, and triethyleneglycolmethylvinylether.
 15. The method ofclaim 14 wherein said glycol vinylether is diethylene glycol vinylether.
 16. The method of claim 13 wherein said monomeric mixture furthercomprises an aldehyde reactant or neutralizer.
 17. The method of claim10 wherein said aldehyde reactant or neutralizer is selected from thegroup consisting of hydrogen peroxide, hydroxyethylethylene urea andL-arginine hydrochloride.
 18. The method of claim 17 wherein saidaldehyde reactant or neutralizer is 2-hydroxyethylethylene urea.